Furnace construction



Jan, 6,1942. E. G. BAILEY v 2,258,558

l FURNACE CONSTRUCTION I 'Filed June 16, 19:58 2 sheets-sheet 1 Fi 5C y U0 E i affin- An-unuuu 12,6 I

i INVENTOR.

ATTORNEY.

Jan. 6, 1942. E. G. BAILEY v 2,268,558

FURNAGE 'CONSTRUCTION l Filed Jupe 16,;*19'38 2 sheets-sheet 2 i51- 2 W OOOOOOO O OQ O j) O O O 000000 50- H "V108, 52.-

46 `4&5

INVENTOR.

ANFORNEY.`

Patented Jan. 6, 1942 i i UNITED STATES PATENT OFFICE 2,268,558 FRNACE coirs'rlmc'rlorz` Ervin G. Bailey, Easton, Pa., asslgnor to The Babcock & Wilcox Company, Newark, N. J., a corporation of New Jersey y Application :une 16,1938, serial No. 214,001

1 claims. (c1. 12a-s) In furnaces: and specifically steam boiler furnaces. These metallic faced water walls may naces, it is economically desirable to burn the not be acceptable for other reasons, for example.

required amount of fuel with a minimum of exin billet heating furnaces, bare water-cooled cess air in the smallest possible furnace having parts absorb more [heat than is desirable, thus walls which will withstand the severe conditions making it unduly costly to maintain the high imposed without excessive maintenance. These temperatures required in the furnace for delivconditions naturally result in high furnace operery f steel billets or the like at temperatures ating temperatures in a furnace of given size, necessary for forging Aor rolling'. At the other and other things being equal, temperatures are l extreme of operating conditions in these waterhigher inlarge furnaces. lo cooled metallic surface furnaces, there are occa- In some furnaces, the enclosing walls are consions when the intensity of heat application to structed wholly of non-metallic refractory'maa localized section of water-cooled surface is so.

terials having softening and fusion temperatures severe for the necessary metal thickness as to which are higher than furnace operating temresult vin damage to the metal and possibility of peratures. However, the problem of furnace conf i5 rendering the unit neperative- Any 0f these struction and the materials used therefor is not undesirable conditions inevitably result in some limited to temperature alone, as with some fuels, modification to the most economical and efcient particularly pulverized coal, the non-combustible construction and operation of the furnace.

material in the fuel or ash, when at the ele- The above indicated limitations of furnace Vated temperature existing in the furnace, tends walls made entirely of ceramic refractory mateto react chemically with the refractory of the rial. and also thOSe 0f the Opposite type 0f Weil furnace construction which is also at the elevated constructed entirely of Water-C00iefi metal, have furnace temperature. Such reactions result in been recognized. and as a result, a third class of the formation of eutectics or the like, having wall construction-has been utilized which can melting points lower than any one of the conbe designated as composite, employing water' stituent ingredients. It is obvious, therefore, that cooled metallic parts and non-metallic refractory the operation of such furnaces must be limited materials associated in considerable variety.

to temperatures below those at which these These composite constructions have been intendchemical reactions will take place in order to ed to provide adequate resistance to destruction, avoid excessive furnace wall maintenance, and 0n the One hand, and. a Suitable limitation 0f this necessarily results in the modification of heat absorbing` Capacity 0n the Othel` hand. t0 one or more of thev conditions for economical the end that the desired furnace temperatures and emcient construction and operation of the might be attained in furnaces 0f diielent Sizes. furnace. i and in furnaces employing different fuels. It

In some steam boiler furnaces the walls are has been suggested that such composite Walls largely if not wholly metallic, these metallic include spaced metallic water tubes exposed diwells being cooled by the water ofthe boilerrectly t0 the furnace cases and associated Withcircuits. These water-cooled walls are formed ceramic refractory material back of the tubes, by rows of steel tubes, arranged in wall align*- or Vwith the ceramic refractory material filling ment, and in some cases they may be contiguous. the intertube spaces and extending toward the When the water tubes are spaced apart, metallic furnace. In Other CaSeS it has been SuggeSted side extensions may be arranged to close the that the water tubes be entirely covered with spaces between them, or the spaces between the a Ceramic refractory facing extending between ltubes may be closed by metallic blocks. Such the tubes and over the furnace sides of the tubes water-cooled metallic furnace walls resist detoa Specified thickness'- struction indefinitely so long as the cooling is Of the composite furnace wall constructions,

adequate, and this is true regardless of the tememploying both Steel tubes and Ceramic refreeperatures of the furnace .and compositions of tory materials. one type has proven to be most the gaseous and incombustible constituents of Satisfactory as to resistance to destruction under the fuels. These constructions are, however,` not severe Operating COnditiOnS. furnace temperature universally acceptable because they may lower control through wall heat absorption adjustment,

the furnace temperatures excessively by the abcost, and such adaptability as to shape-and locasorption of heat by the wang. Furnace tem-. tion that it lends itself readily to advantageous peratures may be too low for stability of flames use in the construction of side walls. roofs, floors', f

or for good combustion, especially in small furarches, baille's. slag Screens. and Other furnace components. This'most desirable water wall type has metallic extensions welded to the tubes along their intertube sides and,l in some cases. also radially with respect to the tubes and hence arranged so that theydiverge outwardly toward `\the furnace face.

' The successful use of this most.desirable form of composite refractory and steel tube-construction applicable to furnace walls requires some means to hold the refractory material in its operative position after shrinkage, or after the formation of cracks in the material.` One (factor that influences the displacement of the furnace of steel or alloy studs of round section, secured i wallrefractory is a layer of slag resulting from the incombustible in the fuel adhering to the furnace face and stickyor semi-plastic when hot, but shrinking and exerting a warping or pulling force on the refractory when it cools. Such a displacement of the ceramic refractory is essentially that of mechanical removal. The ash forming the incombustible portion of a fuel such as n coal has a melting point that naturally varies with its specic chemicalcomposition and consequently the ash from different kinds of coal varies in melting temperatures over a relatively wide range. [Ihe ceramic refractory material must be of such chemical composition that at the temperature of the exposed face, there will be no detrimental chemical reaction between the ash even when it is molten, and the refractory material at its reduced temperature resulting from its proximity to the iluid cooled tubes. In addition, there must be some means of bonding the refractory to the studded metal structure that will also resist the effect of repeated heating and cooling of the wall.

. My invention involves a new combination of materials for the above indicated type of composite wall construction, and it also involves a method of bonding these materials to produce a composite wall of fluid cooled metal with a refractory face that meets service requirements including that of preventing physical or mechanical detachment as Well as chemical erosion or removal of'the refractory beyond an equilibrium thickness during the operation of the furnace. For the metal parts of the composite wall, I preferably employ ferrous metals which may lbe cast iron. wrought iron, cast or forged carbon or alloy steel, according to the shape and pressure requirements of the cooling uid within the metallic parts. I also preferably employ a ferrous metal for the welded extensions of the outer.

surfaces.` For the ceramic refractory, I preferably employ a chrome ore composition prepared or'processed vso as to form a stiif plastic for application to the face of the cooled ferrous metalf and around the metallic extensions of its surface. The chromite of this composition is a spinel and Dart of the iron and chromic oxide canbe re-f placed by either silica or `alumina. so that the minem may vary widely in analysis but maintain its distinctive refractory properties. In all of its various compositions it contains a substantial amount of iron and it is not only highly refracy tory, butl it is essentially neutral in chemical composition and resists chemical combination with combustion products including molten ash. Itis consequently serviceable to a high degree, and of long life. The chrome ore refractory composition includesl material such as water-glass to give it sufllcient plasticity for the purpose of installation and the required initial "air setting.

My method of bonding the plastic refractory to the metal involves the heating o f the furnace face 'of the refractory material after the application of the plastic to the tubes. When the construction is being employed in a furnace in which a fuel is being burned at such a rate to insure such a high temperature being obtainedin actual operation, this heating can be accomplished during the early stages of normal operation'of the furnace. In other furnaces. however, where the fuel being burned and the general combustion conditions will not result in the required high temperature for bonding during normal operation-as for example furnaces in which waste liquor from the sulphate pulp making process known as black liquor is being burned-this bonding is accomplished by heating the furnace to the desired temperature by means of a supplemental fuel, such as oil, prior to normal operation of the furnace. or by local application of heat to successive wall areas to accomplish the 'same effect. Oil or natural gas are desirable fuels for this purpose in View ofthe low ash content of the former fuel and the absence of ash in the latter fuel, this being desirable in view of Ithe possible chemical actions between the molten ash, andthe hot refractory previously referred to. When the furnace face of the wall is heated to a sufficiently high temperature, the refractory composition becomes permanently bonded to the metal extensions on the water-cooled tubes. The bonding, therefore, is a temperature effect at the junction of the chrome orerefractory composition and the ferrous oxide which is naturally adherent to ferrous metal, and this occurs where the temperature has been high enough to bring about some oxidation at the surface of the metal and the sintering of this oxide with the chrome ore. This zone of suiliciently high temperature is limited by the cooling action on the ferrous metal extensions by conduction to cooling fluid within the tubes `integral with those extensions.

Uncooled or insufficiently cooled -ferrous metal exposed to` furnacegases which normally are oxidizing due to excess air supplied with the fuel' will oxidize or burnf in service. This may also occur when the ferrous metal surfaces are not exposed but are covered with the refractory composition through which the gases may diffuse, shrinkage cracks in the refractory material also providing for the exposure of themetal surfaces. The degree, and rate of oxidation of the metal surfaces varies with'the temperature to which the metal is raised, and at the high temperatures employed in my process the ends of the metallic extensions furthest away from the cooly ing action of the fluid in the tubes with which urally at the highest they are welded.

assauts of the metallic extensions, and yet it may be present in the solid form not yet melted, or in the solid form dueto freezing of' oxide which has previously been melted.

Although the invention as above indicated is especially adapted for use in boiler walls, it presents composite refractory structures which are advantageous in other uses because of its durability and low cost.

The invention will 'be described with reference to preferred embodiments which are illustrated in the accompanying drawings, in which: y

Fig. 1 shows a vertical section of a furnace in which the invention is employed;

' Fig. 2is a vertical section of the Fig. 1 construction taken at right angles to the plane along which Fig. l is taken;

Fig. 3 is a detail view showing adjacent tubes of the furnace wall and illustrating the condition of the furnace wall with the plastic chrome refractory applied to the water tubes and th tube extensions prior to the heating of the composite structure;

Fig. 4 is a horizontal section similar t0 Fig. 3 but illustrating the condition of 'a furnace wall after the heating of the structure in accordance with my invention to provide for the bonding of the composite structure;

Fig. 5A is a horizontal section through a portion of the furnace wall, showing the heat insulating material and the tube supports which maintain the tubes in wall alignment;

Fig. 6 is a diagrammatic view indicating the condition of the completed furnace wall under p certain operating conditions.

are utilized to generate steam in a water tube' steam boiler. u

The furnace walls shown in vertical section in Fig. 1 are dened by rows of spaced tubes I8 and -l2` which are maintained in wall forming alignment by securement to horizontalv buckstays It and I6. The latter are in turn supported by the boiler setting columns I8 and 20.

The tubes I are connected at their upper ends with the header 22 from which the risers 24 extend to the steam space of the separator drum 26'. The fluid circuit through the walltubes is completed by the downtakes 28 which .connect the lower header 30 with the water space of the drum 26. A similar arrangement of headers 82 and 34 and circulators 36 complete a uid circuit through the wall tubes I2.

The remaining furnace walls, shown in Fig. 2. are defined by the rows of spaced tubes'40 `and 42 connected at their lower ends to a floor header 44 and at their upper. ends to the opposite headers 46 and 48. Risers 50 and 62 connect the latter to the steam'space of the drum 26, and downtake circulators 64 establish communication between the water space of the drum 26 and the header 44 to complete the wall cooling circuits through the opposite sets of wall 'tubes 40 and the sockets. Cap-screws 58'and 60 pass through these elements to rigidly secure the tubes in alignment `and the H-beam vsections are held against the buckstays I4 by the clips 62 and 64.

The latter cooperate with the inner flanges 66 of the buckstays to form guideways 68 permitting the tubes to have limited movementsy with respect to the boiler setting framework.

Sheet 4metal casing vsections may extend be-l tween the buckstays and be secured thereto to form a furnace encasement to assist in holding the heat insulating layers I8 and I2in the positions indicatedf The materialof the layer I2- is of such character that it may be installed as a plastic or semi-plastic around the tie-bars 5I e and over the colder sides of the wall tubes. while the layers 'I0 may consist of preformedv blocks or slabs of comparatively low density heat insulation material.

Forwardly of the heat insulation layer 12 the tubes ha've metallic extensions welded thereto. They are shown in Figs, 3, 4, 5 and 7 as round section studs preferably extending radially from the tubes and provided with heads at their ends adjacent the tubes. These heads form shoulders which enhance the welding operation and the operative head transfer characteristics of the completed wall.

Although the inter-tube studs lt and I6 are shown to be of the same length as the face studs 'IB and 8l), the relative lengths will depend upon several factors among which the temperature at which the furnace is to be operated is predominant. The material of the stratum 82 is highly refractory, and I preferably employ a chrome ore composition with which a liquid binder is incorporated to such an extent that the composition may be applied by ramming, tamping or the like against the tubes and around the metallic extensionsnr studs. 'I'he composition may set or air harden enough to retain it in place until it is heated and the steps of my invention are carried out. When rammed into place over the studs and tubes this composition assumes a form similar to' that shown in Fig. 3. Its chemical constituency is such that undesirabl chemical reactions with molten ash or slag of pulverized coal or other .fuels are resisted. Furthermore, the refractory does not react with iron its identity and penetrates|the refractory (under the influence of heat) in a dendritic (or branched) formation to form a bond between the studs and the refractory. The iron oxide on an atmosphere'containing some oxygen, the combustion of the fuel being so regulated' that there is a slight excess of air. The chrome refractory being applied to the structure for a thickness corresponding to the length of studs Welded to the tubes, the ends cf the studs are exposed to this high temperature oxidizing atmosphere and are therefore readily oxidized on the surface of their ends.

In the furnace illustrated in the drawings, the normal operating conditions (the furnace burns black liquor, 50% H2O, 22% ash, 28% combustible, 3500 B. t. u./# A. F.) are such as not to result in the high temperature necessary'to procure the bonding `of the composite structure. Consequently, a preburning operation utilizing a supplementary fuel is 'employed to insure the proper bonding. Forthis purpose, oil burners 90 are inserted throughthe primary air ducts 92. Several of these burners are first used on one side of the furnace for a considerableI period of time and then asimilar operation is carried on with the burners arranged at the opposite side of the furnace. In this manner, the surface of the composite wall structure can besubjected to high temperatures. In other furnaces, burning pulverized fuel, oil, or gas, the use of the burners n provided for normal operation, is satisfactory for the purposes of this bonding operation. Normally the ends of the studs are exposed to furnace gases during this heating operation, and this condition permits the formation of iron oxide on the surface of the studs, which oxide may melt or sinter and diifuse into the refractory. Such a relationship of the studs and they refractory is clearly indicated in-Figs. 3, 4, 5 and 7.

When considerable portions of iron oxide have been formedthey become melted or-sintered and extend into a matrix of therefractorymaterial in dendritic formations. Thus, a mechanical bonding action occurs which holds the refractory to the iron oxide which, in turn, is bonded to the ferrous metal, the entire structure thus forming an integral wall.

Fig. 4 of the drawings represents the condition of the wall after the heating process, and this figure is intended to indicate the fact that the heating effect penetrates the wall much more deeply at positions between adjioining studs, the cooling action of the studs limiting this eilect along their surfaces.

During the heating operation, shrinkage of the bonding might be such as to accomplish the heating operation with oxidation of the stud ends and the dendritic formation of iron oxide into the ceramic refractory matrix with little or no alteration in the thickness of the layer of refractory material and with the formation of a relatively thin layer of solidified slag thereon, the furnace face of this solidified layer being molten; Subsequent operation of the furnace with the same coal but at a reduced rate would naturally result in a decrease in furnace temperature which might, in turn, result in a thickening of the layer (94 and 96, Figs. 6 and 7) of solidied slag superimposed on the refractory surface to a point at which the surface temperature of the slag layer is suflicient to maintain they are diminished in length, before the equivarefractory 82 will result in the formation of small `Pbe burned will, under normal operating conditions, result in. furnace temperatures sufficiently high to result in the bonding of the metallic and ceramic refractory material, as for example with pulverized coal, subsequent operation-will result extensions and depth of lthe layer of ceramic refractory, depending on actual operating conditions. For example, the studs welded to ,the water tube are, forease of manufacture and cost reasons, of the same length. With a certain grade of coal having an -ash with a high fusion temperature the initial operation to accomplish' .in the adjustment of the length of the metallic lent equilibrium temperatureon the Wall surface is again reached. Thus, with the particular set of conditions under consideration the initial length of stud and correspondingthickness of` refractory layer might be greater than that necessary for the maximum rate of operation of the furnace, and under these conditions the wall structure would automatically be reduced in thickness to that suited for maximum rate operation. Operation at any lower rate would result in the thickness of the wall being increased over this minimumv by solidified slag accumulations. In this manner it will be seen that this cornposite structure is self adjusting, and by its very nature at all times reaches an equilibrium condition for the particular load at which the furnace is being operated at any one time. While what has been said refers specifically to temperature alone, it will be, appreciated that analogous conditions will prevail for the chemical constituencies of. the various ash compositions of fuels that might be encountered in different installations of i essentially the same design, or in the same installation at diiferent times. l

It will also be appreciated however, thatwhenever the thickness of the refractory layer and lengthv of studs are reduced due to such conditions the temperature effect on the composite structure beyond that which is being removed is essentially the same, and functions the same; as the original heating operation to accomplish' this bonding. In other words, the formation of the oxide on thelmetallic extensions, and the dendritic permeatiox of the oxide into the matrix of ceramic refractory isA accomplished in the vicinity -of the minimum equilibrium thickness so that the bonded surface presented to the furnace at this equilibrium thickness is always essentially the same irrespective of what the minimum thickness, equilibrium temperature, chemical composition of ash, or rat of operation of the furnace might be. The furnace and boiler installation shown in Fig. 1 of the drawings includes a bank of horizontally inclined steam 4generating tubes. ill

connected at their'upper ends to uptake |08 and at their lower ends to downtake |02. The lower ends of the downtake headers are connected to a lower cross header |04 and their upper ends are connected by the tubes |06 with the water space of the drum 26.' The uptake headers |00 have their upper ends connected by the horizontal circulators H with the steam space of the drum 26. The furnace gases pass across the bank of tubes |00 and then into contact with the tubes of the superheater Ill which receives steam from the drum 26. In the particular steam generating installation shown, there are three gas passes across the bank of tubes |00, these" gas spaces being separated by the intervening ballles ||2 and H6.

Fig. 1 also shows a fuel line |20 leading to a spray lburner |22 which is utilized during the normal operation of the furnace. During such operation, recovered chemicals are collected upon the hearth |24 and are drawn from the furnace through the spout |26.

It is understood that while I have found chromev` ore to be a suitable refractory for use in my composite wall construction, my invention Pincludes the use of other refractory of similar properties as to resistance to chemical attack of the slags of ash of solid fuels, and the oxide of iron, in the solid or molten state, and also as to refractoriness or resistance to damage due to temperature alone, and the property of bringing about a bonding of the slag (or refractory) to the metallic oxide, which oxide is bonded to the 'metallic extensions, and thereby holds the rethe tubes, circulating a fluid cooling medium through the tubular parts heating .i the furnace face portion of said molded composition to such a high temperature as to oxidize parts of the said extensions and bond the composition thereto,

and correlating said circulation and the heat ing to control the extent of the oxidation and bonding.

2. In a method of forming a wall 'of a furnace the normal operation of which does not involve temperatures high enough to thermally create chemicallydeveloped bonds between the refractory of the wall and its supporting metal, providing fiuid cooled tubes and securing' them in such position that they will be subject to the heat of the furnace, welding' ferrous metal extensions to the tubes, processing a chemically neutral spinel refractory composition with a plasticizer and cementing agent to form a stiff plastic, molding said stiff plastic composition around the extensions and between the tubes to form an integrated furnace face, .circulating a fluid cooling medium through the tubes, locally heating the-.applied refractory composition at temperatures and over time periods sufilcient to develop thermally and chemically created mechanical bonds between the refractory and the metal extensions to form a thoroughly bonded monolithic wall, the temperature -of such local heating being higher than the normal furnace temperatures during a subsequent operation of the furnace and the intensity and duration of 'the local heating being increased to chemically produce at the ends of the studs irregular bodies bonding the studs with the refractory, said irregular bodies including ferrous substances developed by the local application of the heat to the furnace face, and correlating the cooling and the heating to control the bonding. l

3. The method of forming fluid cooled furnace walls which include stud tubes with refractory material over the furnace sides of the tubes and between the studs, said method including the assembly of the stud tubes in wall formation, the subsequent application of refractory material overv the .furnace faces of the tubesand between the studs, said application of -the refractory material being effected in such a way that the ends of the ferrous metal studs are exposed to the interior of the furnace, the circulation of a copol-l lng fluid through the tubes, the application of heat to the furnace side of the wall with an excess of air and the consequent oxidizing of the ends of the studs, the continued application of heat at a temperature sufiicient to fuse the iron oxide and cause it to bond with the refractory material by extending into a matrix of that material in dendritic formation, and the correlation of said heating with the cooling effect of said circulation, the cooling of the refractory material by the circulation of fluid through the tubes'during normal operation of the furnace solidifying some of the previously molten iron oxide in such dendritic bonding formations.

4; The method of forming a corrosion resistant wall for a furnace normally operating at temperatures -below the fusion point of iron oxide, the method comprising the pressure molding or cementing of a stiff plastic chrome ore refractory and plasticizer mixture around and between spaced ferrous metal elements so that the refractory is packed tightly between these elements, leaving the ends of said elements exposed toward the interior of the furnace, subjecting the furnace face formed by the molded refractory and the exposed ends of said ferrous metal elements to the heating and drying action of combustion under oxidizing conditions to cause the formation of iron oxide at, the ends of said elements, increasing the intensity of said combustion and thereby fusing the `developed iron oxide and causing it to flow into cracks lin the refractory and thus mechanically bond said elements and the refractory in an integral monolithic furnace wall, cooling the opposite ends of said ferrous elements by fluid circulation while said combustion is being effected, and correlating said cooling andheating to control the extent of the iron' oxide fusion and consequently control the bonding, the furnace thereafter operating at temperatures normally below the fusion temperature of the bondingviron oxide.

5. In the art ofbuilding furnaces, the method which comprises the application of a chemically neutral refractory in a moldable condition to wall tubes having ferrous extensions thereon,

causing a' fluid cooling medium to be circulated through the tubes, and simultaneously applying heat to the furnace face of the refractory and causing a cooling medium to be circulated through the tubes to bond said ferrous extensions and the refractory, said bonding resulting at least in part from the development of iron oxide on the extensions and the subsequent fusing or sintering of the same with the refractory, the cooling effect of said medium and the heating being correlated to control the bonding and limit said fusing or sintering.

6. In the art of building furnaces, the method which comprises the molding of a chrome ore refractory composition to a row of vstudded tubes to combine with the ends of the studs to present a furnace face, the furnace ends of the studs being left uncovered in the disposition of the refractory, simultaneously heating the refractory and the stud ends and applying the cooling effect of a 'fluid circulation to the tubes and their studs to form a monolithic wall, the intensity of the heating being increased to produce irregular bodies at the furnace ends of the studs to bond the studs to the refractory, the bonding of said irregular bodies being limited by said cooling effect to positions near studs.

'1. In the art of building furnaces, the method which comprises the arranging of a plurality of ferrous metal extensions in good heat exchange relationship to a hollow ferrous structure adapted to contain a flowing cooling medium, installing a moldable chromite base refractory composition over said body and .around the extensions, oxidizingthe ferrous metal of the extensions by the application of heat to the furnace face of the refractory and thereby developing iron oxide between the refractory and the outer ends of extensions while cooling the tubes and the tube ends of the studs by circulating a cooling fluid through thev tubes, and fusing the iron oxide at least a part of which is subsequently the outer ends of the lsolidied to bond the extensions and the refractory.

ERVIN G. BAILEY. 

